Numerous devices for venting and relieving excess pressure and vacuum conditions in containers such as storage tanks and the like are well known in the art. Among the known devices are separate pressure relief valves and vacuum vent devices which can be individually selected and installed in separate openings in a container to meet pressure relief and vacuum make up air requirements. A limitation of using separate pressure and vacuum relief devices is that either two orifices must be available on the container device for mounting the separate vent devices, or a manifold or Y-shaped adapter for mounting both devices in a single container orifice must be used. Other known devices that combine pressure and vacuum relief are also known in the art. Such devices, however, suffer from various limitations including providing flow rates of make up air for vacuum relief which are insufficient to compensate for the conditions produced when using relatively large and powerful pumps to remove products from a container to prevent the collapse or implosion of the container.
Another combined pressure and vacuum relief vent construction includes seal means between the vacuum relief means and a central shaft portion thereof, which seal means can leak and fail so as to prevent the accurate and reliable operation of the device at precise pressure and vacuum conditions. An alternative is to open the fill or access cover of a storage container during removal or filling of product to relieve the undesirable pressure condition. Limitations of this procedure are exposure of the contents of the container to contamination from the surrounding environment, exposure of the personnel to the contents, and also the danger of failure to replace the cover when the filling and emptying operation is complete. Contrasted to the relatively limited devices and alternatives discussed above, the subject invention relates to a rather uncomplicated, precise and reliable combination vent device for relieving excessive pressure and vacuum conditions in a storage or like container.